The present invention generally relates to an electric motor, and more particularly, to a method for driving a three-phase stepping motor.
In recent years, there has been a tendency that stepping motors come to be used for automobiles, and the stepping motor as an automobile component is required to be compact in size, with higher torque and less vibration.
FIG. 5 shows driving current waveforms for respective coils in a micro-step driving of a conventional three-phase stepping motor, in which the current following through a first coil is represented by Numeral 31, the current flowing through a second coil, by Numeral 32, and that flowing through a third coil, by Numeral 33.
In FIG. 6, there is shown a circuit block diagram for micro-step driving of a conventional three phase stepping motor, which generally includes instruction input terminals 34 connected, through error amplifiers 35, to drivers 38, which are further coupled to the motors 41 connected with current detecting resistors 40, and a triangular wave oscillator 36 coupled with the drivers 38 through a level shift circuit 37, with current feedback amplifiers 39 being coupled between the terminals 34 and the motors 41 connected to the resistor 40 as shown.
By the above arrangement, sine waves respectively shifted in phase by 120.degree. are inputted to the terminals 34 as the instructions. Each of the current detecting resistors 40 is inserted per coil one phase to effect the current detection for each one phase, and the current thus detected is applied to the error amplifiers 35 through the feedback amplifiers 39. Thus, the motor current is controlled by constituting the current minor loop. The drivers 38 are constituted by a transistor H bridge which allows current to be fed to each phase, and respectively subjected to the PWM (Pulse Width Modulation) control. The level shift circuit 37 is provided with a rest period for preventing arm short-circuiting of the transistor H bridge. By arranging as described above, the motor current synchronized with the instruction value may be controlled, and thus, it becomes possible to subject the three-phase stepping motor to the micro-step driving.
However, in the known arrangement as described above, there is such a disadvantage that the current detection must be effected for the micro-step driving, thus requiring the current detecting resistors. Moreover, the circuit construction becomes complicated for constituting the current minor loop, with a consequent rise in cost. Furthermore, there has been such a problem that due to the complicated circuit construction, the circuit tends to be large in the scale, and can not be employed for application into small spaces.